Human cytomegalovirus (HCMV) is a ubiquitous pathogen for the developing embryo (especially affecting the developing CNS), and also causes life-threatening diseases in immunodeficient adults including cancer patients and AIDS victims. Human teratocarcinoma stem cells (embryonal carcinoma, or EC, cells) differentiate into a variety of somatic cell types, including neurons, and provide an invaluable model in which to study the regulation of cell differentiation in a way pertinent to early embryogenesis. HCMV replicates in some of the differentiated derivatives of EC cells, but not in the EC cells themselves. We are investigating the effects of HCMV infection on this model system, to determine how HCMV interacts with permissive and non-permissive cells, and how it may disrupt normal cell differentiation. HCMV infection of differentiated teratocarcinoma cells and human fibroblasts leads to the induction of the cell surface antigen stage-specific-embryonic antigen-1 (SSEA-1); in the teratocarcinoma cells the expression of ganglio-series glycolipid antigens, normally induced during differentiation, is reduced in infected cells. There is evidence that SSEA-1 is involved in cell-cell interactions crucial for normal embryogenesis. Thus the ability of HCMV to induce inappropriate SSEA-1 expression may bear strongly on its ability to disrupt normal embryonic development. We propose experiments to determine the biochemical and genetic basis of SSEA-1 induction by HCMV, as well as changes in the expression of other differentiation antigens. We shall use transfection with cloned fragments of the HCMV genome of identify the part of the viral genome responsible for such changes and ascertain whether this is an early or late viral function. In the differentiating teratocarcinoma system we shall determine which differentiated cells (e.g., neurons and their precursors) are permissive, partially permissive and non-permissive for HCMV. We shall also investigate whether SSEA-1 induction is common to all cells following HCMV infection and what other changes in surface antigen expression are induced. Finally we shall determine how HCMV infection of differentiating EC cells, and its effects on surface antigen phenotype of the cells, may alter their course of differentiation, especially in relation to the neuronal lineage.